In lithography techniques, for example, a resist film composed of a resist material is formed on a substrate, and the resist film is subjected to selective exposure of radial rays such as light or electron beam through a mask having a predetermined pattern, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film.
A resist material in which the exposed portions become soluble in a developing solution is called a positive-type, and a resist material in which the exposed portions become insoluble in a developing solution is called a negative-type.
In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of pattern miniaturization.
Typically, these miniaturization techniques involve shortening the wavelength (and increasing the energy) of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are now starting to be introduced in mass production. Furthermore, research is also being conducted into lithography techniques that use an exposure light source having a shorter wavelength (and higher energy) than these excimer lasers, such as F2 excimer lasers, electron beam, extreme ultraviolet radiation (EUV), and X ray.
Resist materials for use with these types of exposure light sources require lithography properties such as a high resolution capable of reproducing patterns of minute dimensions, and a high level of sensitivity to these types of exposure light sources.
As a resist material which satisfies these conditions, a chemically amplified resist is used, which includes a base component that exhibits changed solubility in an alkali developing solution under the action of acid and an acid generator component that generates acid upon exposure.
For example, a chemically amplified positive resist typically contains a resin component (base resin) that exhibits increased solubility in an alkali developing solution under the action of acid, and an acid generator component. If the resist film formed using this resist composition is selectively exposed during formation of a resist pattern, then acid is generated from the acid generator within the exposed portions, and the action of this acid causes an increase in the solubility of the resin component in an alkali developing solution, making the exposed portions soluble in the alkali developing solution.
Currently, resins that contain structural units derived from (meth)acrylate esters within the main chain (acrylic resins) are widely used as base resins for resists that use ArF excimer laser lithography and the like, as they exhibit excellent transparency in the vicinity of 193 nm (for example, see Patent Document 1).
Further, in order to improve various lithography properties, a resin having a plurality of structural units can be used as the base resin. For example, in the case of a positive-type resist composition, a base resin containing a structural unit having an acid-dissociable, dissolution-inhibiting group that is dissociated by the action of the acid generated from the acid generator, a structural unit having a polar group such as a hydroxyl group, a structural unit having a lactone structure, and a structural unit having a glycidyl group is typically used (for example, see Patent Document 2).
Further, in order to reduce the occurrence of developing defects, a chemically amplified positive resist composition in which an epoxy compound (a non-polymer) having a molecular weight of approximately 100 to 1,000 is included together with the base resin has been proposed (see Patent Document 3).